Demand for bandwidth in lightwave communication systems is ever increasing. This increasing demand can be met by installing additional fiber cable. However, augmentation of existing long distance fiber systems is costly. Thus, it is desirable to use existing systems to maximum capacity.
One technique for increasing the capacity of an existing fiber system is a form of space division multiplexing in which two optical signals of different polarizations are simultaneously transmitted through a single optical fiber. Simultaneous transmission of different data sequences in the same fiber via a separate polarization for each sequence permits doubles the amount of information passing through the fiber. However, polarization mode dispersion and nonlinear effects in the fiber will cause two simultaneously transmitted optical signals to interfere with each other. For example, polarization mode dispersion and nonlinear effects induce phase changes and power dependent distortion in the polarized optical signals as the signals pass through the fiber. This, in turn, makes the two interfering optical signals difficult to distinguish from each other. Inability to distinguish between the signals makes it difficult to exploit the second, orthogonal polarization dimension to achieve higher information rates by space division multiplexing of the signals.